- Author: Whitney Brim-DeForest
In the past year, the California rice industry has begun to deal with a new pest: “weedy rice”, also known as “red rice”. Weedy rice is a common weed in rice-growing regions of the world, and when infestations are high, it can significantly reduce yields. In the southern USA, losses have been as high as 60% when uncontrolled. In 2016, through the efforts and cooperation of rice growers and Pest Control Advisors, weedy rice has been identified on over 10,000 acres in Butte, Glenn, Colusa, Sutter, Yuba, Placer and Yolo counties. Although 10,000 acres may sound like a lot, it is still only a small percentage of the total rice acreage in California (about 2%).
What makes "weedy rice" unique is that it is the same species as domesticated rice (both are Oryza sativa L.). This means that growers can only control weedy rice through non-chemical means, since any herbicides applied to control the weedy rice will also kill the crop. In the California rice cropping system, where chemicals are the primary method of weed control, growers can use cultural practices such as as a stale seedbed before the rice season. However, this can delay planting by as much as a month. Alternatively, growers can fallow or rotate with another crop, and if the infestations is high, this may be the best option. During the growing season, if weedy rice is found in the field, the only option that growers currently have is to hand-pull it out.
How does a grower know if they have weedy rice? Weedy rice can be identified before flowering, when all grass-control herbicides have been applied:
- If grassy weeds remain in the field, check for an auricle and ligule (see photo below).
- If none are present, then the grassy weed is likely a watergrass species.
- If an auricle and ligule are present, it may be weedy rice, and it is time to get help with identification. A PCA or UCCE Rice Advisor should be able to assist in identification.
Once rice has headed (produced seed), weedy rice panicles and the panicle of the crop will look similar, so growers should look for any that are different than the planted variety. Again, a PCA or UCCE Rice Advisor can assist in identification. If the field is a certified seed field, then the California Crop Improvement Association (CCIA) should be called to identify the suspect plants.
Many growers have asked why it is important to control weedy rice, since weedy rice is still rice, and therefore, edible. There are a number of ways that weedy rice can impact rice production:
1) Reducing milling quality: Due to the extra milling required to remove the red-colored bran, the number of cracked and broken kernels will increase, therefore decreasing the value and the price paid to the rice grower. If the rice is to be milled and sold as brown rice, large amounts of red bran can reduce the milling yield significantly.
2) Hybridization with domesticated varieties: Weedy rice can cross with domesticated varieties in the field. If there is a high number of weedy plants in a field, the odds that this will occur is even greater. The hybrids (between weedy rice and domesticated varieties) may have different characteristic than their parents (more vigorous growth, for example).
3) Yield decreases: Since weedy rice shatters (falls off of the panicle before harvest), once the population reaches a critical threshold in the field, yields can decrease significantly.
4) Weed management cost: Weedy rice cannot be managed by chemical means. Therefore, any control efforts have to be through cultural practices. One of the most effective methods is to hand-pull it out of the field. Labor, as we all know, is very expensive.
Weedy rice is a manageable pest in California rice, but it will only be possible through the joint efforts of rice growers, PCA's and members of the rice industry. It will take accurate identification in the field, as well as timely and sustained control efforts in the field.
WHERE & WHEN
Richvale: Thursday, Jan. 26, 8:30 am, Evangelical Church, 5219 Church St., Richvale
Glenn: Thursday, Jan. 26, 1:30 pm, Glenn County Office of Education, 311 South Villa Avenue, Willows
Colusa: Friday, Jan. 27, 8:30 am, Colusa Casino Resort, 3770 Hwy 45, Colusa
Yuba City: Friday, Jan. 27, 1:30 pm, Veterans Hall, 1425 Veterans Memorial Circle, Yuba City
TIME: Doors open at 8:00 am and meetings start at 8:30 am at Richvale and Colusa. Doors open at 1:00 pm and meetings start at 1:30 pm at Glenn and Yuba City.
8:00 a.m. (1:00 p.m.) Doors open, sign-in, coffee
8:30 a.m. (1:30 p.m.) Call meeting to order - Nominations – Dana Dickey, Rice Research Board
8:35 a.m. (1:35 p.m.) Rice Pesticide and Regulatory Update – County Ag Commissioner
8:50 a.m. (1:50 p.m.) Weedy Rice in California – Whitney Brim-DeForest, UCCE
9:20 a.m. (2:20 p.m.) New Rice Seed Policy for RES Varieties – Kent McKenzie, RES
9:40 a.m. (2:40 p.m.) Arthropod Management Update – Luis Espino, UCCE
10:00 a.m. (3:00 p.m.) Fertility Update – Bruce Linquist, UCCE
10:30 a.m. (3:30 p.m.) Weed Management Update – Kassim Al-Khatib, UCCE
11:00 a.m. (4:00 p.m.) — ADJOURN —
**** 1.5 DPR Credit in the “Other” category and 2 CCA CE credits****
Finally, the armyworm season seems to be over. Moth trapping shows that the numbers are decreasing to the lowest levels of the season. Additionally, most fields are ripening and therefore less susceptible to armyworm injury.
Overall, armyworm infestations were not as severe as last year. At the beginning of the season there were some very early infestations; however, those infestations may have been detected early because growers and PCAs were scouting closely after last year's outbreak. In most cases, the early infestations that were brought to my attention consisted of small worms, which usually go unnoticed until a few weeks later in the season.
In late August, a second infestation peak occurred. However, this infestation was similar to what we see in normal years. Nevertheless, I saw some injury that might have been approaching treatment levels.
The armyworm moth trapping conducted this year started a little later than I wanted. Next year I hope to start trapping in late May or early June so the first armyworm peak can be detected timely. Number of moths trapped remained low until August, when they started to increase and reached a peak in all locations in the Sacramento Valley. The moth peak observed in early to mid August corresponds to the increased injury observed in late August, when eggs laid by those moths reached the 3rd and 4th instars.
- Author: Whitney Brim-DeForest
The 1st Annual Rice Weed Course will take place:
Friday, September 16, 2016
from 8:30AM to 4:15PM (Registration begins at 8:00AM)
Hamilton Road Field (on West Hamilton Rd. between Hwy. 99 & Riceton Hwy.)
and Rice Experiment Station, Biggs, CA
The day will begin with an interactive tour of the Weed Science research plots at Hamilton Road. Participants will also spend time learning about weed identification for important rice weeds both at emergence and at heading. Presentations will cover emerging pests of rice, such as weedy red rice and winged-leaf primrose willow. Attendees will hear about new pesticide registrations and updates to current pesticides, as well as information regarding the new Butte herbicide. This course is also a great opportunity to interact directly with the UCCE and UC Davis Rice Weed Research Team!
For a full agenda and registration go to:
For questions, please contact Whitney Brim-DeForest at 530-822-7515, or by email at email@example.com
Credits for PCA, QAC, QAL, Private Applicator, and CA Certified Crop Adviser are pending.
Our two year stretch of little to no blast might be over. I visited an M-209 field last week that seemed to be infected with blast. The lesions appeared to me like propanil drift burn; however, the yellow halo around the lesions made the PCA suspicious. Paul Sanchez, pathologist at the Rice Experiment Station, collected some leaf samples and was able to confirm it is blast.
According to Paul, changes in environmental conditions may be why the lesions did not look like your typical blast lesions. When conditions are favorable, the fungus' spores germinate and infect the tissue. But if conditions change and become unfavorable for the fungus growth and sporulation, the fungus dies and the tissue then has that burned look instead of the white-gray powdery look.
Some of the lesions did look more like the typical blast lesion.
M-209 is a variety closely related to M-205, a variety considered to be susceptible to blast. Since we have not seen blast in the field since M-209 was released, we do not know what level of susceptibility M-209 has. This might be the year we find out.
At this point, a fungicide treatment is not recommended. However, a treatment near heading may be appropriate considering that the field and area have a history of blast epidemics./table>